1'3 Measuring Angles

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1.3 Measuring Angles

• Stone High School Geometry

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Objectives

• Measure angles with a protractor.
• Identify and use the Angle Addition Postulate.

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Defining Angle Measure

• A protractor is used to measure angles. As on a
  ruler, the intervals of a protractor must be
  equal. Then you can be sure that if the two
  angles have the same measure, then they are
  congruent.

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Look at example 1
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• Angles are measured in degrees.
• A protractor may thought of as another type of
  geometry ruler.

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Angle Congruence Postulate

• If two angles have the same measure, then they
  are congruent. If two angles are congruent, then
  they have the same measure.

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Example 3
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Angle Addition Postulate

• If point S is in the interior of angle PQR, then
  measure of angle PQS measure of angle SQR
  measure of angle PQR.

Q
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Pairs of Angles

• Complementary angles are two angles whose
  measures have a sum on 90º. Each angle is called
  the complement of the other.
• Supplementary angles are two angles whose
  measures have a sum of 180º. Each angle is
  called the supplement of the other.

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Example 4 Name all complementary and
supplementary angle pairs below.

• Measure of angle A is 60 degrees
• Measure of angle B is 30 degrees
• Measure of angle C is 120 degrees.

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Linear Pair Property

• If two angles for a linear pair, then they are
  supplementary.

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Classification of Angles

• Definitions Three Types of Angles
• A right angle is an angle whose measure is 90
  degrees.
• An acute angle is an angle whose measure is less
  than 90 degree.
• An obtuse angle is an angle whose measure is
  greater than 90 degrees and less than 180 degrees.